Motors are not only being widely used in home appliances such as a washing machine, a refrigerator, an air conditioner, a vacuum cleaner, and the like but are also being used in an electric vehicle, a hybrid vehicle, and the like, which are recently gaining attention.
Among types of motors, a permanent magnet motor that uses a permanent magnet rotates a rotor using a magnetic interaction between a magnetic field generated by a coil through which a current flows and a magnetic field generated by the permanent magnet.
A driving apparatus such as an inverter capable of applying a driving voltage is required to drive the permanent magnet motor. Since a magnetic field generated by the rotor of the permanent magnet motor is determined in accordance with a position of the rotor, the inverter has to apply a driving voltage in consideration of the position of the rotor.
In addition, an alternating current (AC) power having a set frequency is supplied to households and businesses. Compared to this, the motor driving apparatus supplies an AC power capable of changing a frequency and level to the permanent magnet motor, thereby rotating the permanent magnet motor.
For this, a commercially used AC power is rectified to be converted into a direct current (DC) power, and the DC power is reconverted into an AC power of a desired frequency and level using the driving apparatus such as the inverter.
Here, an electrolytic capacitor is widely being used for stabilizing the DC power rectified from the AC power. However, the electrolytic capacitor has a problem of having a short life. Also, although a high-capacity capacitor is used to supply a stable DC power, the high-capacity capacitor has a problem of having a large volume.